Art. Sensors Orthosis Art. Controller Motor ProsthesisExample Skeletal CNS Muscles system Phys. Sensors EMG-activated prostheses • lower extremities: controlled damping, no motor, artificial sensors • upper extremities: myo-electric arm prosthesis, motor, no artificial sensors
Art. Sensors Orthosis Art. Controller Motor ProsthesisExample Skeletal CNS Muscles system Phys. Sensors
Art. Sensors Orthosis Art. Controller Motor ProsthesisExample Skeletal CNS Muscles system Phys. Sensors Otto Bock C-leg
Prosthetic foot design passive mechanism: • damping 10 J • energy storing?? • No actuation!
Concepts of gait• Walking is: – preventing to fall – cyclical movement with left/right foot placements in front of the other supporting body weight• The purpose of bipedal walking is to maximize the double support time while maintaining the forward velocity.• Stability is maintained by balancing the trunk through coordinated actions of joints.
Double support phase
Stilt walkingPelvic tilt: ±35°
Stilt walking + feetPelvic tilt: ±15°
Stilt walking + feet + kneesPelvic tilt: ±0°
Normal walking(feet, knees, ankles, pelvic rotation) Pelvic tilt: free
Why is d.s. phase important ? slow walking• Largest ground right left total reaction forces 1,4• largest muscle forces reaction force [-] 1,2 1 0,8• almost all mechanical 0,6 0,4 work 0,2 0• stable position 0 20 40 60 time [% stride] 80 100 other phases are more or less ballistic Maximize double support time !
Prosthetic / orthotic gaitWalking without knee function would result in…• Reduced velocity• Reduced double support time• Reduced step length• Increased pelvic tilt
Balancing mechanism • direct ground reaction force (push against large mass of trunk) • trunk will rotate (a little) • requires coordinated joint actions
Trunk movement in walking Fast walking Normal walking Walking with large steps